1. Field of the Invention
The present invention relates to a method and to an apparatus for depositing a layer on a semiconductor wafer by vapor deposition in a process chamber. The invention relates, in particular, to the deposition of an epitaxial layer composed of silicon on a semiconductor wafer composed of monocrystalline silicon, and to an apparatus suitable therefor.
2. Background Art
Semiconductor wafers are often provided with a layer produced by means of vapor deposition. The semiconductor wafer is usually held by a rotating susceptor during deposition of the layer, the susceptor being arranged in a process chamber. Upper and lower covers which are transmissive to thermal radiation and through which radiation energy is transmitted into the process chamber and onto the semiconductor wafer form boundaries of the process chamber. The semiconductor wafer is heated to a specific temperature that is optimal for deposition of the layer. The process chamber furthermore has connections on the side walls for introducing process gas into the process chamber and for discharging process gas and gaseous products of the process gas from the process chamber. The process gas is conducted over the face of the semiconductor wafer that is to be coated. Upon contact with the semiconductor wafer which has been heated to the deposition temperature, process gas is decomposed and the desired layer is deposited on the semiconductor wafer.
It is necessary to clean the process chamber at specific intervals, because it is not possible to completely prevent products of the process gas from depositing in the interior of the process chamber, for example on parts of the susceptor, the inner surface of the upper cover, or the inner side of the side walls. Cleaning is effected by means of vapor phase etching, for example.
Semiconductor wafers cannot be coated during cleaning of the process chamber. Therefore, there is a great interest in having to clean the process chamber as infrequently as possible.
For this reason, EP 0 808 917 A1 recommends controlling the temperature of the walls of the process chamber within a narrow temperature range in a control loop.
It specifically proposes cooling the process chamber by means of a cooling gas from outside and controlling the temperature of the walls by controlling the inflow of cooling gas to a target temperature.
In accordance with U.S. 2007/0042117 A1, control of the temperature of the surface of the process chamber can be extended, for example, by controlling the temperature of the upper cover of the process chamber and the temperature of the lower cover of the process chamber independently of one another. For controlling the temperature of the covers and the temperature of the substrate to be coated, use is made, inter alia, of pyrometers, which measure the temperature of the upper cover on the outer surface of the upper cover, the temperature of the lower cover on the outer surface of the lower cover, the temperature of the substrate in the center of the front side of the substrate and the temperature of the susceptor carrying the substrate. The control loop also comprises a cooling system that conducts a cooling gas against the upper and lower covers.